**5.6 Integrating the heating tubes**

Building the digester is associated with integrating the heating tubes. Building the wall starts with structuring the iron grids which will be encased by wood panels or preconstructed metal sheets, and before pouring the concrete, the heating tubes should be integrated (Figs. 11 and 13). The heating tubes are made of polyvinyl chloride (PVC), inside these tubes hot water flows to heat the digester. The water temperature is either 35 oC or 55 oC depending on the used bacteria as either mesophilic of thermophilic bacteria, respectively. On the other hand, in other designs the heating tubes are installed on the internal surface area of the digester wall.

Biogas Plant Constructions 357

The technology that should be installed includes the filling indicator, tubes, measuring devices and meters, electricity network, fiber cables …etc. Afterwards, the gas collector should be installed as well as the excess and low pressure safeguard and the air support fan.

(a) MT-ENERGIE GmbH & Co. KG (b) BIOGAS NORD GmbH

This is the process of lining the digester by mortar or using sheets of foam as in Figure 17. This is one of the most important construction steps and should be carefully and accurately achieved. In case of lining, the process is performed using mortar containing 1% silica. After the completion of the lining, the digester is painted using the petroleum Albumen. In other designs, the walls are heat insulated with a clad with non-corroding and weather-proof aluminum trapezoidal panels. On the other hand, the rural digesters are coated with layers

Fig. 15. Mesh network that supports the gas holder of a household unit

Figure 16 shows an overview of the technology installation.

**5.8 Technology installation** 

Fig. 16. Technology installation

**5.9 Installing the insulation** 

of dry dirt and asbestos.

Fig. 13. Integrating the heating tubes (BIOGAS NORD GmbH)
